The present invention relates to a method of and an arrangement for pre-heating coal in general, and more particularly to such a method and arrangement as used for pre-heating coal to be supplied to a coking oven.
Various pre-heating arrangements and methods have already been proposed. In the coking industry, the pre-heating of the coal to be supplied to the coking oven by passing the coal, entrained in a stream of gaseous carrier medium at a high temperature, through a one or two stage conveying riser in which the carrier medium yields heat to the coal and thus pre-heats the same, has found widespread acceptance. When it is desired to dry the coal, for instance, by heating the same to about 90.degree. C., it is usually sufficient to use a one-stage arrangement; on the other hand, when it is desired to heat the coal to a temperature as high as 250.degree. C., it is recommended to use a two-stage type system in which the coal is dried in the first stage until the moisture content thereof is reduced to 1 to 2%, while the coal achieves a temperature of 85.degree. to 90.degree. C. Then, the moisture liberated from the coal in the first stage is withdrawn from the pipe system, and the coal is additionally heated in a second stage or pipe which is arranged downstream of the first stage or pipe.
Attempts have already been made to accomplish the entire pre-heating operation for the coking coal, to a final temperature of the coal of about 250.degree. C., in a single conveying riser. However, under these circumstances, in order to be able to elevate the temperature of the coking coal to the desired level, it was necessary to adjust the input temperature of the carrier medium to such a high level that, as a result of the spontaneous water evaporation in the moist coking coal, a large part of the coal granules or bodies disintegrated or burst. In addition thereto, oxidation of the coal took place, which resulted in a highly undesirable impairment of the capability of the coal to sinter during the coking operation.
However, it has been now established that it would be very advantageous if the pre-heating of the coking coal to temperatures above 130.degree. C., preferably 150.degree. to 250.degree. C., could be accomplished in a single conveying riser, if it could be assured that the above-discussed disadvantages of the prior-art approaches can be avoided.